On Mon, Dec 20 at 19:19, Edward Ned Harvey wrote:
If there is no correlation between on-disk order of blocks for different disks within the same vdev, then all hope is lost; it's essentially impossible to optimize the resilver/scrub order unless the on-disk order of multiple disks is highly correlated or equal by definition.
Very little is impossible. Drives have been optimally ordering seeks for 35+ years. I'm guessing that the trick (difficult, but not impossible) is how to solve a "travelling salesman" route pathing problem where you have billions or trillions of transactions, and do it fast enough that it was worth doing any extra computation besides just giving the device 32+ queued commands at a time that align with the elements of each ordered transaction ID. Add to that all the complexity of unwinding the error recovery in the event that you fail checksum validation on transaction N-1 after moving past transaction N, which would be a required capability if you wanted to queue more than a single transaction for verification at a time. Oh, and do all of the above without noticably affecting the throughput of the applications already running on the system. --eric -- Eric D. Mudama edmud...@mail.bounceswoosh.org _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
